1. Field of the Invention
The present invention relates to a liquid droplet jetting apparatus such as an ink-jet printer.
2. Description of the Related Art
An ink-jet printer as an example of a liquid droplet jetting apparatus, includes an ink-jet head which jets ink droplets supplied from an ink tank, toward a recording paper from nozzles. This ink-jet head is provided with a channel unit which makes jet ink droplets from a plurality of nozzles, and an actuator (such as a PZT) which generates a pressure for jetting the ink droplets as described in US Patent Application Publication No. 2007/0182787 (corresponds to Japanese Patent Application Laid-open No. 2007-203482) for example. A plurality of surface electrodes provided on an uppermost surface of the actuator, and an electrode land of a flexible wiring member such as an FPC (Flexible Printed Circuit) and a COF (Chip On Film) are connected via an electroconductive adhesive such as solder.
Moreover, joining the ink-jet head including an actuator and a channel unit to a flexible wiring member by solder is not quite preferable, since an effect of a heat, which is imparted to the actuator and the channel unit at the time of melting the solder in a high-temperature environment as in a reflow process, is substantial. Moreover, due to unevenness of an actuator surface and curling of the flexible wiring member, there is a variation in a distance between electrodes. Therefore, for joining assuredly the melted solder between the electrodes, instead of the reflow, it is necessary to absorb a variation in a solder height by heating and pressing from above a wiring member by a bar heater as described in US Patent Application Publication No. 2007/0182787.
Incidentally, at the time of connecting the electrodes of an electronic equipment etc. in general, solder or solder paste melted by heating is interposed between the electrodes. Sometimes, the excessive solder outflows from a gap between the electrodes, and moves to other electrode portion, and induces a problem of short-circuit etc. Therefore, various proposals have hitherto been made for preventing the short-circuit due to the excessive solder.
For instance, in a soldered structure of an electronic circuit unit of Japanese Patent Application Laid-open No. 2004-79872, a circuit board and a mother board having patterns thereon respectively are stacked up and down to be connected mutually. The circuit board has a first resist layer and the mother board has a second resist layer to protect the respective patterns, and by removing a part thereof, each land is provided. A wall portion made of an insulating material is arranged between the resist layers, surrounding each electrode land. Accordingly, even when the solder applied on the land is melted in the reflow step, it is possible to prevent the excessive solder from leaking out.
In recent years, in an ink-jet head as disclosed in US Patent Application Publication No. 2007/0182787, a size reduction, an increase in the number of channels (multi-channel use), and a high densification have been carried forward. In accordance with this, since a plurality of surface electrodes is arranged highly densely in a limited surface area of the actuator, a distance between adjacent surface electrodes has become extremely narrow. Therefore, when an excessive solder between the surface electrode and the electrode land is leaked out, the leaked solder easily reaches the adjacent surface electrode, and a possibility of the short-circuit between the circuit electrodes becomes even higher.
Moreover, in the soldered structure in Japanese Patent Application Laid-open No. 2004-79872, as shown in FIG. 5, a wall portion 13 and a second resist layer 12 are arranged to surround a second land of a mother board 58, and carry out a function of holding solder provided to a first land by the wall portion 13 and the second resist layer 12. However, regarding the surface electrode (which is the second land) on the actuator (which is the mother board) of the ink-jet head according to the soldered structure of the Japanese Patent Application Laid-open No. 2004-79872, since the surface electrodes are arranged highly densely, and the gap between adjacent electrodes is extremely narrow, it is not practical to provide a structure such as the second resist layer 12 or the wall portion 13 on the actuator, and it is difficult to ensure a reliability of the electrode. Therefore, a solution for a problem of short-circuit, due to flowing of the excessive solder from a gap between the surface electrode and the electrode land which are arranged on the surface of the actuator has been sought further.
Moreover, in a case of the structure described in Japanese Patent Application Laid-open No. 2004-79872, the electrode land stacked up and down have the same area, and by highly densifying the electrode lands, a solder space formed by the electrode land, the resist, and the wall portion becomes small. In other words, a connecting area (an electrode surface and an exposed area of the land) of the solder becomes extremely small, and it is necessary to apply a solder of a fine diameter (extremely small amount). However, due to the extremely small amount of solder, there has been a problem that a variation in the amount is occured.
Moreover, since the connecting area of the land becomes small, and the amount of solder becomes extremely small, there may occur a case, in which the land is not joined appropriately to the surface electrode. Furthermore, due to the unevenness of the actuator, the curling of the flexible wiring member, and the contamination of the electrode surface, it is difficult to join appropriately, mechanically and electrically by absorbing the variation in the distance between the land and the electrode by the solder. Moreover, when the amount of solder becomes large, since a solder space between the land and a terminal is small, there is a risk of the solder leaking out beyond the wall portion. Furthermore, since the distance between adjacent surface electrodes is small, the short-circuit is susceptible to occur.
Moreover, in the ink-jet head, when the heating temperature is low and when there is a deviation in a pressure applied at the time of heating and pressing for melting the solder, a mechanical joining strength becomes insufficient. In this case, an exfoliation of a joint portion and a variation in joints of solder are occurred during use or during a manufacturing process. Whereas, when the heating temperature is high and the pressure applied is high, the solder leaks out to the surface of the actuator from the gap between the surface electrodes which are stacked face-to-face, and the solder which has leaked reaches the adjacent surface electrode. Therefore short-circuit tends to occure.
In this manner, in the ink-jet head in which a large number of channels are arranged highly densely, due to the solder space (connecting area) which connects, becoming small, it becomes difficult to control the amount of solder, the heating, and pressurizing. Therefore, even when the structure as described in Japanese Patent Application Laid-open No. 2004-79872 is used, it is not possible to prevent completely the short-circuit between adjacent electrodes by controlling the variation in the joints.